The Formation of Lehman Caves

Cave Origin

Our understanding of the origin of Lehman Caves has changed a great deal over the last few years due to additional research. Here is an excerpt from Louise Hose's 2018 "The Geologic Story of Lehman Caves."

 

The Pole Canyon Limestone formed about 550 million years ago near the equator.

Image created by The Design Minds.

The basic geology of Lehman Caves can be broken down into four main parts:

1. Formation of the Pole Canyon Limestone, which contains Lehman Caves. This rock layer began as limestone that originated from a warm, shallow sea about 550 million years ago near the equator. This limestone layer was covered and uncovered periodically. Later, the rock layers drifted north to their present location. When the Basin and Range province was made, the rock was put under a lot of heat and pressure, making it into a low grade marble. The mountain-building phase created many fractures in the rock.

 

The Pole Canyon Limestone moved to eastern Nevada and was fractured through mountain-building processes. Then warm, acidic water rose from below and dissolved away cavities along cracks.

Image created by The Design Minds

2. Dissolution of the rock to make a cave. Warm acidic water from below (hypogenic) entered cracks in the rock and dissolved away passages and rooms. This left voids in the rock. This dissolution occurred near the top edge of the water table.

 

Calcite deposition on a drop of water.

NPS photo

3. Deposition of speleothems. While the previous phase is sometimes referred to the “hollowing out phase,” this third phase might be called the “filling in phase.” The water table dropped, and as surface water percolated through soil and organic debris and became slightly acidic, it dissolved away part of the marble above the cave. When the calcite-rich water reached the air-filled passages, it deposits speleothems of many types.

 

4. Condensation corrosion. This last phase has only recently been identified. As you go through Lehman Caves, you may notice that many of the speleothems look like they’ve been eaten away. This is due to air, seasonally high in carbon dioxide, dissolving away speleothems and marble. This process may only have started within the last ten thousand years, as the climate got drier.

 

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Computer generated model showing the passages of Lehman Caves

NPS IMAGE